1. Field of the Invention
The invention relates to a method and system for monitoring the flight of a golf ball after impact with a golf club head, and particularly to computer-controlled estimation of golf ball flight, impact timing and transfer efficiency characteristics.
2. Discussion of the Related Art
Golf swing and golf ball flight monitoring have been used as tools for golf instruction and for testing golf equipment such as golf clubs and golf balls for many years. Such details as club head angle and club speed at impact with the ball, as well as club take-away and downswing path, are known to be crucial in determining ultimately important ball flight characteristics, such as distance, direction, backspin and ball flight curvature after impact. However, a golf swing is simply too fast in real time for clear human observation of its many subtle features.
High speed cameras and/or other sensors have been used to sense and record data about the golf swing and/or initial ball flight characteristics. The data is often displayed for slow speed analysis of a golfer's form during the swing by an instructor and/or the golfer him or herself. The position of the golfer's shoulders, hips, legs and/or head, as well as his or her arms and hands, throughout the golf swing hive been captured on high speed still, video and televisions cameras either in a series of still frames or in videos or movies replayable in slow motion. Some such techniques are described, e.g., at U.S. Pat. Nos. 4,713,686, 5,111,410 and 5,210,603.
Besides capturing the data described above of the golfer's form, data of the path of the golf club head during the swing and initial characteristics of the golf ball in flight after impact with the club head are often used. These latter data are more often used for determining total ball flight characteristics such as distance, direction and curvature, rather than the golfer's form, and are arguably more relevant factors than form for determining the performance and effectiveness of a golfer's swing. Moreover, equipment such as the golf club and golf ball being used can be tested using these latter data, whereas the golfer's form really doesn't affect such performance of the golfer's equipment. Computer processors running software algorithms are often used for calculating or more of the above-mentioned features or others of the complete ball flight from the sensed and recorded data.
A series of United States patents assigned to Acushnet Company, makers of Titleist™ golf equipment show and describe various techniques and equipment for testing and determining golf club and golf ball performance using measured pre-impact and post-impact characteristics of the golf club and golf ball. These patents include U.S. Pat. Nos. 4,063,259, 4,136,387, 4,158,853, and 5,471,383.
For example, a pair of light source-photodetector pairs are positioned as described in the '259 patent at spaced-apart locations alongside the plane of the golfer's swing. Light emitted by each light source is received by its corresponding photodetector unless an object breaks the line of the emitted light to the detector. As the golf club head nears the golf ball in a test method according to the '259 patent, the club head swings through the line of sight of a first detector to the emitted light from its corresponding light source. When this happens, a signal is sent to a camera shutter to open. Just before the club head impacts the golf ball, a second line of sight of a second detector and its corresponding light source is broken. At this time, a second signal causes a xenon lamp to flash such that the reflected light is captured by the camera whose shutter was previously opened.
Next, a microphone captures the sound of impact of the golf club head with the golf ball. This acoustic signal is amplified and used as a trigger for a second xenon lamp to flash such that a post impact image of the golf ball is captured by the camera as shutter remains open. The same amplified acoustic signal is sent through a delay and is used as a trigger for a third xenon lamp to flash such that another image post-impact image of the golf ball in flight is captured by the camera. Shortly thereafter the shutter of the camera is closed, and a still frame having three images is stored on a film.
The use of a microphone to detect an acoustic signal requires setting up and maintaining of the microphone, as well as precise positioning and calibration separate from the optical components of the system. Also, the sound of impact of the particular golf ball and club at the test station where the microphone is being used has to be distinguished from other club-ball impacts going on in the vicinity of the microphone as well as from other sounds emanating from and around the test area. It is desired to have a golf ball flight monitoring system that does not use an acoustic photoflash trigger, and instead preferably uses all photosensitive equipment.
The film including the three temporally successive images of the golf ball reveals some useful initial characteristics of the flight of the golf ball. For example, the initial launch angle and velocity of the ball in the image plane can be respectively determined from the center of gravity positions of the successive images of the golf ball, and the known time duration between the capturing of the first and second or second and third images on the film.
A mark placed on the ball prior to performing the test can be used, as described at the '259 patent, to reveal the amount of backspin initially imparted to the ball by the club head. This initial backspin is determined based on how much the mark is observed to have rotated in the plane of the film from the first to the second and from the second to the third images of the ball captured on the film.
One way to find the backspin based on the captured images is to measure manually or by sight and experience the relative orientation of the mark between two successive images. Using the known timing between capture of the two images, the rate of backspin can be calculated. This procedure can consume a great deal of swing evaluation time and its accuracy is unreliable. Moreover, a calculation of such results of the backspin as loft during flight of the ball cannot be determined quickly as is desired during valuable swing evaluation time.
The small single mark described and shown in the '259 patent may not be visible if side spin causes the mark to rotate to the “dark” side of the ball, i.e., away from the camera side of the swing path. It is also difficult to distinguish the backspin from the sidespin imparted to the ball using the small single mark.
Lynch et al. were not concerned with sidespin in their description in the '259 patent because a mechanical golfer was used that presumably did not impart any sidespin to the ball at impact. Also, the mechanical golfer was presumed to hit the ball straight ahead with each test swing so that the initial direction of the golf ball was not considered as a factor in any of the tests described in the '259 patent. Moreover, it is understood that the '259 patent is drawn to equipment testing and not to analyzing swing characteristics of a golfer. Thus, such ball flight characteristics as the amount of fade or draw (or hook or slice, as the case may be) that a golfer is achieving due to the sidespin the golfer is imparting at impact, or the initial direction of the ball struck by the golfer, are not addressed in the '259 patent. It is desired to have a ball flight monitoring system and method that does determine ball flight characteristics based in part on the initial horizontal direction of the golf ball's flight and the initially imparted sidespin on the ball, in addition to the initial vertical flight conditions and backspin on the ball.
Each of the '387, '853 and '383 patents describes the use of one or more highly reflective or contrasting marks in the form of spots or dots on the golf ball for determining initial post-impact spin characteristics of the golf ball. Using subsequent images of the one or more spots, each of these patents sets forth some description of how to determine the complete spin characteristics of the golf ball, and not simply the backspin as discussed above with respect to the '259 patent. However, the one or more spots may again not be visible to the camera if they are rotated to the dark side of the ball when the image is captured on film. In addition, any dirt or scuff mark on the ball may not be distinguishable from the spots in a practical apparatus being used for multiple swings in the field.
The '387 and '853 patents disclose to position three cameras or photosensors each at ninety degree spaced locations around the golfer for detection of the mark or marks wherever they may turn around the golf ball. The three photosensors cannot be combined to achieve a single planar image of the initial flight of the ball and the data captured by the three photosensors is processed according to a complex algorithm that factors the rotationally spaced locations of the sensors. Also, the angular spacings of the sensors has to be very accurate or the calculated spin characteristics of the ball will be unreliable. It is desired to have a method and system for determining the complete initial spin characteristics of the golf ball without having to sense marks on the ball in more than a single observation plane.
The '383 patent sets forth a method for determining the total spin imparted to the golf ball using six highly reflective marks or spots on the ball and capturing their relative motions at successive temporal points within a single film frame. Data of the relative positions of the six marks as captured on the film is converted to data directly related to the total spin on the ball using a complex algorithm as described in the '383 patent. However, any one or all of the marks could again be rotated during a real golf swing to the dark side of the ball in which case the calculations would fail because the input data would be incomplete.
Gobush et al. are again concerned in the '383 patent with equipment testing, and not golf swing analysis, and thus the mechanical golfer used in the tests described in the '383 patent never imparts an amount of sidespin to the ball sufficient to cause any of the marks to rotate to the dark side of the ball before all of the camera images are captured. It is desired to have a system and techniques for determining total spin imparted to a golf ball notwithstanding the degree of sidespin on the ball.
The field of golf swing analysis is also understood in the present invention to be lacking systems and techniques that measure and/or determine or calculate and utilize data of the golf club head prior to impact with the ball in conjunction with initial flight characteristics. Such pre-impact club head data is desired, e.g., for determining energy transfer efficiency between the club and ball, whether any sidespin or horizontal ball directional characteristics are imparted by club head angle or swing path characteristics, and for obviating the need for acoustic sensing of impact for triggering image capture. It is also recognized in the present invention that such a desired system and techniques would be useful for golf swing analysis as well as for testing equipment, including such testing for determining the unique equipment specifications of particular golfers depending on their individual swing characteristics.
It is therefore an object of the invention to provide a golf ball flight and golf swing monitoring system and technique wherein pre-impact swing plane direction and head angle characteristics of the take away and downswing of the golf club are measured and analyzed.
It is a further object of the invention to have a system and technique for determining the total initial spin imparted to a golf ball, including backspin and sidespin, and also preferably the three-dimensional initial flight direction of the golf ball after impact with a golf club using a single frame including multiple temporally successive images.
It is also an object of the invention to have a golf ball flight and golf swing monitoring system and technique that combines pre-impact swing characteristics with initial flight conditions of the golf ball to determine transfer efficiency characteristics.
It is another object of the invention to provide a system and technique for monitoring and analyzing initial ball flight characteristics using a trigger for precisely timing the capture of temporally successive images.